Phương trình đường thẳng Δ_1

a_1.x + b_1.y + c_1 = 0

Phương trình đường thẳng Δ_2

a_2.x + b_2.y + c_2 = 0

Góc giữa hai đường thẳng Δ_1 và Δ_2

cosφ\;=\; \frac{ |a_1 \dot a_2+b_1 \dot b_2  | }{  \sqrt{ a_1²+b_1² } \sqrt{ a_2²+b_2² }  } 

Δ_1 ⊥ Δ_2 ≅  \vec{ n_1 } ⊥ \vec{ n_2 } ≅ a_1 a_2+b_1 b_2=0

a_1 = -0.1 (slider from -10 to 10, step 0.1)
b_1 = 7.8 (slider from -10 to 10, step 0.1)
c_1 = -0.5 (slider from -10 to 10, step 0.1)
Δ_1: a_1 * x + b_1 * y + c_1 = 0.0
a_2 = -1.3 (slider from -10 to 10, step 0.1)
b_2 = 1.6 (slider from -5 to 5, step 0.1)
c_2 = -3.1 (slider from -10 to 10, step 0.1)
Δ_2: a_2 * x + b_2 * y + c_2 = 0.0
M = Intersect(Δ_1, Δ_2)
A = Point(Δ_2)
B = Point(Δ_1)
a = OrthogonalLine(B, Δ_1)
b = OrthogonalLine(A, Δ_2)
C = Intersect(a, b)
φ = Angle(B, M, A)
D = Point(a)
E = Point(b)
n_2 = Vector(A, E)
n_1 = Vector(B, D)
α = Angle(D, C, A)